Chromatographic techniques in the downstream processing of proteins in biotechnology.

The purification of the product, the so-called downstream process (DSP), tends to be one of the most costly aspects of modern bioprocessing, especially in the case of proteins. In such cases, chromatography is still the major tool on all levels of the DSP from the first capture to the final polishing step. In this chapter, we will first outline the commonly used methods and their setup, in particular ion exchange chromatography (IEX), hydrophobic interaction chromatography (HIC), affinity chromatography (AC), and gel filtration (GPC, SEC), but also some less-known alternatives such as hydroxyapatite chromatography (HAC). Then the rational design of a downstream process, which usually comprises three orthogonal chromatographic steps, is discussed. Finally, process variants deviating from the usual batch-column/gradient elution approach will be presented, including expanded bed, displacement, and continuous chromatography, but also affinity precipitation. A most recent trend observable in the biotechnical DSP is the drive towards disposable elements (single-use technologies). Some options for this will be discussed as well.